Styrene monomers are capable of radical, cationic and anionic polymerizations owing to a resonance effect of a phenyl group thereof, differently from the other monomers. Moreover, since synthesized polystyrene polymers may be easily reformed and have excellent formability characteristics, the styrene monomers have been widely studied and thus commercialized.
Numerous researches on the styrene monomers have continued to progress since an anionic polymerization of styrene was developed. Moreover, since the styrene monomer having a functional group such as a hydroxy group, an amine group, a sulfur group, and the like causes various side reactions during the polymerization process due to a strong reactivity of an activated carbanion, various researches aimed at solving the problem have also continued to progress.
For example, a method of anionically polymerizing a styrene derivative having an electron donating group such as —CN, —NO2, —COCH3, —COOBut, —CONEt2, etc. as a functional group in a para position has been mainly reported. However, it has been reported that, if the styrene derivative having an electron donating group such as —CH3, —OCH3, —NH2, —N(CH3)2, etc. as a functional group in a para position is anionically polymerized, the yield of polymerization is decreased due to an addition reaction caused by a strong reactivity of an carbanion or the molecular weight and molecular weight distribution are not controlled. In this case, the functional group should be protected by an appropriate protecting group. That is, the styrene monomer having the functional group such as an amine group, a hydroxy group, a ketone group, a sulfur group, etc. in a para position is protected by the appropriate protecting group such as trimethylsilyl, t-butylmethylsilyl, oxazoline, an ester compound, etc. to be polymerized using the anionic polymerization and then the functional group is separated from the protecting group [Seiichi Nakahama and Akira Hirao, Prog. Polym. Sci., 1990, 15, 299., Akira Hirao, Surapich Loykulnant, Takashi Ishizone, Prog. Polym. Sci., 2002, 15, 299. T. Ishizone, G. Uehara, A. Hirao, and S. Nakahama, Macromolecules, 1998, 31, 3764. T. Ishizone, T. Utaka, Y. Ishino, A. Hirao, and S. Nakahama, Macro-molecules, 1997, 30, 6458, T. Ishizone, G. Uehara, A. Hirao, S. Nakahama, and K. Tsuda, Macromolecules, 1998, 31, 3764.].
Meanwhile, there has been reported a method of anionically polymerizing after reducing the reactivity by forming a complex and coordinately bonding with an additive such as lithium chloride, diethylzinc, dibutylmagnesium, etc. [Christian Schade, Macromol. Chem. Phys., 1999, 200, 621., Y.-S. Cho, J.-S. Lee, Macromol. Rapid Commun. 2001, 22, 8, 638., R. P. Quirk and Y. Lee, J. Polm. Sci. Part A, 2000, 38, 145.].
In a case where the monomer is solid, it is difficult to completely remove impurities existing in the monomer. Accordingly, there occurs a problem in that the activation of an initiator is reduced by the impurities existing in the solid monomer. Moreover, the solubility of the solid monomers becomes an issue in terms of the fact that most anionic polymerizations are typically carried out at low temperatures.
Moreover, there have been reported numerous research results in which complexes are synthesized in the form of a monomer with metal compounds such as iridium using phenylpyridine and phenylpyridine derivatives and then applied to organic electroluminescent elements. Examples of studying energy transfer phenomena using the same have been publicly known in the art. As a relevant prior art, a phenylpyridine is polymerized to form complexes with iridium and various metal compounds and then organic electroluminescent characteristics were measured [L. S. Hung, C. H. Chen, Materials Science and Engineering R, 2002, 39, 143., Maria C. DeRosa, Derek J. Hodgson, Gary D. Enright, Brian Dawson, Christopher E. B. Evans, and Robert J. Crutchley, J. AM. CHEM. SOC., 2004, 126, 7619., Albertus J Sandee, Charlotte K. Williams, Nicholas R. Evans, John E. Davies, Clare E. Boothby, Anna Kohler, Richard H. Friend, and Andrew B. Holmes J. AM. CHEM. SOC., 2004, 126, 7041, M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest, Appl. Phys. Lett., 75, 4, (1999), Raymond C. Kwong, Sergey Lamansky, and Mark E. Thompson, Adv. Mater., 2000, 12, 1134., K. Dedeian, P. I. Djurovich, F. O. Garces, G. Carlson, R. J. Watts, Inorg. Chem., 1991, 30, 1687-1688., King, K. A, Spellane, P. J., Watts, R. J., J. Am. Chem. Soc., 1985, 107, 1431.].
As described above, most metal complexes containing phenylpyridine are limited to organic monomers. Meanwhile, there has been reported a result of studying electroluminescent characteristics in a manner that vinyl groups are introduced into phenylpyridine to synthesize polymers having side chains of phenylpyridine through a radical polymerization and then complexes are formed with iridium and various metal compounds. Moreover, there has been reported a result of investigating electroluminescent characteristics in a manner that polymers having main chains of phenylpyridine are polymerized through a Suzuki coupling reaction and then complexes are formed with iridium.
Conventional problems such as a phenomenon in which an organic monomer material is decomposed by heat generated from an organic electroluminescent element when an organic monomer is applied to the organic electroluminescent element and an aggregation phenomenon occurring in the material have been solved by introducing a polymer form into an organic metal complex. However, the organic complex in the form of the polymer synthesized by the radical polymerization that is different from the organic monomers having a regular molecular weight showed a decrease in the electro-luminescent efficiency due to the irregular molecular weight.